text:
How would modern jet fighters engage and defeat prop driven fighters?
How would modern jet fighters engage and defeat prop driven fighters?  Assuming all things being equal (avionics, weapons, etc), if the two aircraft were co-altitude in a level merge, what tactics would the jet use to quickly overwhelm his adversary?

If I remember correctly, Chuck Yeager used to demonstrate dogfighting jets in his Mustang, and winning

A modern jet would fire an AIM-120D from 50 nm then go home or find another target.

Or you could just turn on full afterburner and run away...

Like this https://youtu.be/oyjNInIH4Hw?t=3m56s

Merge
Assuming neither aircraft tried for a head-on guns snapshot, the goal of the jet against the prop will be to go out of plane with the prop post merge and deny the prop a quick guns solution.  By far the easiest way for the jet to go out of plane is to extend and then take the fight vertically.  This means that the jet is in full AB coming into the merge and well above cornering speed, while the prop is coming into the merge at its best corning speed hoping to get a quick snapshot.  As the aircraft approach both pilots tighten down and pass as close as possible to prevent either aircraft from taking angles right after the merge (ie, so that neither aircraft has a turning advantage immediately post merge).
Post Merge
As the aircraft make their first pass, the prop (knowing full well the jet will take the fight vertically) begins a max performance turn hoping to quickly take angles and give itself a quick snapshot against the jet as the jet climbs.  However, the jet, knowing the prop is looking for a radius fight, extends the merge horizontally, at Mach 1+ and then begins a supersonic climb upwards.  Due to the lower thrust to weight ratio of the prop, most of the props potential energy comes in the form of its altitude; however, the jet has liquid potential energy in the form of fuel, and many can accelerate in the vertical, this gives the jet a decided advantage against the prop.  Because the prop cannot climb with the jet, and the jet is now outside of its guns range, the prop must remain at altitude and wait for the jet to attack.
Out of Plane
The jet, moving vertically, has now successfully moved out of plane with the prop rendering the turning radius of the prop moot.  An unchallenged out of plane maneuver is certain victory for the jet.  The jet can now cut the turning circle of the defender from above.  The best hope for the prop is to either pull hard into the jet trying to force an overshoot (and hope that the jet isn't already anticipating this and drawing a wall of lead between this anticipated spot and his current location) or, to wait until the last minute and pull into the vertical with the jet (causing a vertical merge) and hope for a head-on snapshot.  Either way, the jet can quickly disengage vertically again, causing the prop to bleed precious energy with these high G maneuvers, and then reengage when he has the advantage again.  Each time the jet disengages, the prop is left scrambling to regain its depleted energy, and the jet is maneuvering to prevent the prop from ever being able to fully recover.  This means that as the prop dives to gain speed, the jet dives after it, forcing another high G pull from the prop for another overshoot, or, if the prop tries to extend horizontally, the jet attacks again, forcing the prop to use more energy.
Conclusion
The jet will either force a mistake out of the prop and kill it, or the prop will eventually run out of altitude and airspeed and either auger into the ground, or be killed when he doesn't have the energy to force the overshoot, or climb vertically again.  This, of course, ignores things like thrust vectoring, and the flight computers, in aircraft like the super hornet, which give certain Gen 4/5 aircraft supermaneuverability--meaning, post merge, most Gen 4/5 aircraft could just out rate the prop and the fight would likely be over in seconds.

@keelerjr12 you've got to remember, there are no training rules in real life.  Forward quarter gun shots, merges under 500ft, everything is legal when someone is actively trying to kill you.  In this scenario, as the prop, I'd have to assume a high aspect kill was my only option, and as the jet I'd be fighting to deny that shot.  You're going to have to have a fluid game plan in real life, and if your opponent is obviously looking for a forward quarter shot then you'll have to adjust accordingly.  In training though, as you know, the mid air risk precludes those shots.

In an actual encounter, much depends on how much fuel each adversary has left. If no pilot makes a dumb mistake, the one with the longer flying time wins.

@PeterKämpf That rarely happens, even among fights between like aircraft, with equal load outs and equal fuel. Somebody always makes an error (however minor), its the human condition.  I've seen fights stagnate, but there always seemed like there would be an eventual winner.

That’s certainly a good strategy if the fight is limited to gun kills only.  But in an age of BVR radar guided missiles and close in high off boresight IR missiles, a look-shoot-zoom scenario might place the jet in considerable danger.  Of course, assuming both aircraft have similar weapons systems aboard, it would be equally risky for the propeller driven aircraft as well.

Note: This answer is from the original version of the question, which specified a P-51 and an F-22.
What chance would a P-51 have against an F-22?  None whatsoever.
The F-22 pilot would spot the P-51 on radar as soon as it came over the horizon, pop off an AIM-120D or similar missile at a range of 100 miles, and depart, without the P-51 ever coming within engagement range.  The P-51 pilot would probably never even be aware of the presence of the F-22.

This is a valid answer to the current question. But I think "close-quarters" was meant more than "subsonic."

But I think "close-quarters" was meant more than "subsonic." Yes. In a dogfight.

This answer is only valid for permissive RoE that allows a BVR engagement.  You might want to offer that caveat.  (It is otherwise IMO very succinctly put).  No need to shoot at 100 miles.  The chances of being seen at 30 - 50 are pretty small, particularly given the speed advantage F-22 has in terms of choosing an approach angle (more or less with sun behind them) before taking the shot.

How would modern jet fighters engage and defeat prop driven fighters?

If you'd asked that question some decades ago, the answer might have been:
They might not ...

Rather than pull away and make a hasty retreat to the safety of their carrier’s air defense net, the four pilots broke formation and turned towards the eight approaching jets, ready to give the enemy pilots the fight they were itching for. Drawing upon one of the most reliable maneuvers taught to pilots at the time, the four pilots began moving in scissor patterns, attempting to draw their pursuers into an overshoot while presenting themselves to be difficult, if not impossible, targets to get a good bead on. Each pilot was aiming to get into position for a high deflection shot if the opportunity presented itself. The eight MiGs split up into groups of two, each flying after two Sea Furies. Neither group of aggressors were able to hit their quarry, owing to the practiced skill of the four Royal Navy pilots. In the fray of the battle, one MiG, broken away from his flight, screamed towards Carmichael. This time, there would be only room for a split-second action, and Hoagy took it, loosing a burst of cannon fire in the MiGs direction as he rushed past. Banking and then jinking away, Carmichael was unable to get a clear picture on his recent foe, but from radio chatter presumed that Sub-Lt. Haines managed to get a fairly decent hit on the same fighter too. After the third and fourth pilots in the formation, Lt. Pete Davis and Sub-Lt. Brian Ellis hurled more lead in the direction of the retreating MiG, the stricken aircraft began spewing an incredible amount of smoke. It then veered sharply off course and smashed into the ground, ending the day for the remaining MiG pilots.

https://tacairnet.com/2015/02/23/british-sea-furies-and-migs-in-korea/

“I fired a short burst at the MiG and missed, but got the MiG pilot’s attention. He turned into us, making a head-on pass. Charlie and I fired simultaneously as he passed so close that Charlie thought I had hit his vertical stabilizer with the tip of my tail hook. Both of us fired all four guns. Charlie’s rounds appeared to go down the intake and into the wing root, and mine along the top of the fuselage and through the canopy. He never returned our fire, rolled, inverted, and hit a small hill, exploding and burning in a farm field.”

https://theaviationist.com/2015/01/14/the-most-unusual-mig-killer-the-skyraider-air-to-air-victories-on-north-vietnamese-mig-17s/

In BVR, the engine is irrelevant - he who sees first, shoots first. In a gun fight, jet engines do not offer a significant advantage over ICE and some people would even argue that they are not an advantage at all. How well do you think an F-22 would do at the Reno air races? Faster speeds just means slower turns which means more predictable targets. A good pilot will use whatever advantage they have, and an given that an F-22 has less than 5 seconds of gun, I would not give them strong odds.

Mark's answer covers what would happen in a real world scenario.
However, assuming that they've somehow accidentally got into range of each other... the F-22 pilot wasn't paying attention etc. And also assuming somehow that they have the same weapons and avionics, then one of the following would probably happen

Both aircraft have the weapons/avionics of the P-51

The F-22 climbs. It has a climb rate HUGELY in excess of the P-51. Once above the P-51, it can "Boom and Zoom" against the P-51 all day. Dive in behind, open fire, climb away again... without ever being in a tiny amount of danger. By the time the P-51 turns to point its guns at where the F-22 was, the F-22 has rocketed away (like literally, by comparison, rocketed). The F-22 simply repeats this until the P-51 is dead.

Both aircraft have the weapons/avionics of the F-22

Assuming a head-on pass, the F-22 detects the P-51 long before the P-51 even knows an F-22 is nearby. The F-22 blows the P-51 out of the sky.
Assuming the F-22 misses and they pass each other, are at a comparable speed, and assuming that from now on either can get a lock on the other with equal chance, the F-22 simply uses its vastly superior maneuverability to turn in behind the P-51, fires another missile and casually leaves after again blowing the P-51 up.

The aircraft are in entirely different leagues.

the F-22 simply uses its vastly superior maneuverability. How more maneuverable is a F22 against a P51 mathematically? Isn't a lower turning radius any plus to the Mustang?

The P-51 doesn't have a lower turning radius, or even close. The F-22 is astonishingly maneuverable due to it's thrust vectoring.

We're talking about an impossible scenario, I don't think 'exactly true' is really all that vital

It's worth noting there is a difference between the turn rate, the degrees per second the nose can move and turn radius, the actual size of the circle.  Having a smaller radius doesn't always matter.

@keelerjr12 this answer is for an earlier edit of the question which specified the F-22 vs P-51. Other jets would struggle to perform a similar horizontal turn but their superior power would still probably allow them to perform a vertical turn more effectively


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What are the symptoms of vortex ring state?
What are the signs and symptoms a pilot can recognize, that the helicopter is approaching vortex ring state (VRS) and measures should be taken?
A related question discusses how to prevent or recover from VRS, but it does not address the recognition technique. Similar to stalls (which happen unintentionally), being able to identify a worsening situation before the stall fully develops is better than stall recovery.

You can see the symptoms quite well in this video.  NB, see my comments below as to why this is not settling with power,  it is vortex ring state.

@Simon - I would guess that it started at about :40 in the video, and he'd recovered by about :56?

@FreeMan Exactly.  You see it start to shake then yaw left.  After that, it's like a bone shaker until he flies out of it!

Vortex ring state is characterized by rapid descent and reduced effectiveness of control inputs. At the onset, it is characterized by increased vibration and buffet of the airframe, with uncommanded changes in helicopter attitude. Also, any increase in the collective is ineffective and counterproductive.
From skybrary.aero:

Incipient vortex ring conditions are typically:

increased vibration and buffet,
the onset of small amplitude ‘twitches’ in pitch and evidence of longitudinal, lateral and directional instability.

Established vortex ring conditions are characterised by:

a very rapid increase in rate of descent towards and beyond 3000fpm,
reduced effectiveness of cyclic inputs in roll or pitch
the application of collective pitch failing to arrest the rate of descent and usually increasing it.

From FAA Helicopter Flying Handbook- Helicopter Emergencies and Hazards:

A fully developed vortex ring state is characterized by an unstable condition in which the helicopter experiences uncommanded pitch and roll oscillations, has little or no collective authority, and achieves a descent rate that may approach 6,000 feet per minute (fpm) if allowed to develop.

The best measure against vortex ring state is quite simple- go forward i.e. increase airspeed. Basically, you enter into forward flight so that the rate of descent doesn't oppose the induced flow. You need 'undisturbed' airflow over the rotor disc. Power is to be applied after gaining sufficient airspeed. From skybrary:

Incipient Stage ... Keep the collective position unchanged and apply forward cyclic to achieve an accelerative (nose down) attitude so as to increase forward airspeed quickly. As soon as a steady increase in airspeed is indicated, and above 30 KIAS, more power can be applied if necessary without waiting until the best rate of climb speed is reached.
If this action does not resolve the situation rapidly then it is best to treat the condition as established and take the actions below.
Established Condition. Recovery can only be effected by changing the airflow around the rotor and will inevitably lead to significant loss of height, which makes recovery from a low level occurrence impossible.
There are two theoretically possible actions: Moving the cyclic forward and lowering the collective. Combining these actions is likely to produce the quickest recovery with the least height loss.
Application of forward cyclic should increase airspeed but a large input held for several seconds may be required before significant pitch attitude and consequent speed change is achieved, with a significant nose down attitude resulting. Lowering the collective to reduce power towards auto-rotation, so unstalling some of the inboard portion of the blades, may also be effective but forward airspeed must be gained before power is re-applied during recovery.

Autorotation has also been suggested as a measure for overcoming the vortex ring state (by the FAA handbook, for example), but it may lead to further loss of height, which has to be taken into account. Another issue is that there are some variations between the different helicopter types- in case of tilt-rotor aircraft like V-22, the only way is to go into forward flight.

This defines what it is, but doesn't address the "measures to be taken", could you elaborate?

@RonBeyer I've added it. See if its ok. I'd left it out as the OP clearly said the the linked question discussed recovery.

I read the question wrong as him asking for the measures as well, but I think its good to include here, thanks!

I thought this was called power settling.

@CarloFelicione Oooh, you've opened Pandoras' box.  In most places, vortex ring state and settling with power are used interchangeably, even in helicopter literature.  But they are different states.  Put simply, settling with power is when you don't have enough power to stop a descent.  It is distinct, and aerodynamically different, to vortex ring state.  It can occur when changing from downwind to upwind, when heavy, when overestimating performance etc.

@CarloFelicione  The crucial difference is that you have almost zero chance of recovery since you have simply run out of power.  Power required is greater than power available. It is a limitation brought about by the environment, or pilot action or a mechanical failure.   Vortex ring state typically happens <30kts, >300fpm descent, power on.  Settling with power can occur <300fpm descent.  Watch the debate begin...

@Simon per that other answer, settling with power is not universally agreed as that term, and "power required exceeds power available" is as close to accurate a term ... but that's for the other question/answer. Aeroalias, have you read the article on what actual VRS looks like in a V-22?  After the Murana crash, test pilots went out and found out, at altitude. You might want to refer to that and revise your last paragraph accordingly.

The main rotor of a helicopter enters the Vortex Ring State when it enters its own downwash.  In order for that to happen, it must be producing downwash, have airspeed less than Effective Translational Lift (ETL), and be descending faster than its downwash.
The pilot can recognize that they are approaching the conditions for VRS whenever the aircraft is in powered flight (not in autorotation), airspeed is slow and descent rate is high.
This typically occurs during steep or vertical approaches; normal approaches with a tailwind; or hovering OGE when altitude is not precisely controlled and a descent rate develops.  Accordingly, it is during these maneuvers that the pilot must be most alert to the hazard.
Helicopter pilots are commonly taught that there are three "ingredients" necessary for the main rotor to enter VRS:

Using power
Flying less than 30KIAS
AND
Descending faster than 300fpm

Although these are not hard numbers (in reality, they vary depending on aircraft design, disk loading, ambient conditions, etc.), they are useful warning signs to remind the pilot to guard against VRS.  If a pilot is flying with two of the ingredients, they must take measures to avoid the third.
E.g. When a rapid descent, but not autorotation, is required, the pilot must maintain airspeed above ETL.  When slow flight, less than ETL, is required, the pilot must closely monitor altitude and vertical speed to descend no faster than the downwash (generally around 500-1500fpm, increasing with aircraft gross weight).  If descending rapidly, while slowing airspeed, the pilot must ensure that descent rate is decreased before losing ETL.
Different helicopter designs respond differently to VRS, but there are common symptoms. Generally, when the main rotor begins to enter the VRS, the helicopter will vibrate and begin an uncommanded descent, and controls may lose some degree of responsiveness. Although plenty of engine power is available, increasing power--raising collective--actually makes the condition worse (hence the term used by helicopter pilots in the U.S. to describe what is happening, i.e. Settling With Power). At this stage, the appropriate measures are to lower collective and fly into "clean" air, or ETL, in whichever direction is most appropriate.
Note: any rotor system can enter the Vortex Ring State. Tail rotor VRS is one of the conditions that can result in Loss of Tail rotor Effectiveness (LTE). It is generally assumed when you say VRS, that you mean MR VRS, but it might be useful to clarify.

VRS is settling of a helicopter in its own downwash. Settling rates can be as high as 6000fpm.
To develop VRS you must have all three of the following conditions
1. Speed < ETL.
2. Vertical speed > 300fpm
3. Power on between 20-100%
If any one of these conditions is missing, NO VRS settling.
The best technique to recover from VRS is the Vuichard Recovery. Which is a power ON Side slip to the Right (Counter rotating rotors) or left for Clockwise rotating rotors.

The best technique is to Not Get Into VRS in the first place.  I recommend the detailed discussion here regarding VRS and vuichard's limited case maneuver  ... and the other issue is to know the aircraft that you are flying, and what its VRS profile is.  Claiming "one size fits all" is both irresponsible and dangerous.

I'm sorry, but I don't see how this answers the question "What are the symptoms of vortex ring state?"

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text:
I want to build a flight simulator!
For fun I want to build a flight simulator at home.
What are my options from most basic toy environment to more realistic set-up.
Great if you can give for each solution a basic indication of cost (software / hardware), and if appropriate the space needed.

I've just started building a home cockpit too. I think this question is too broad, but here are the links I've bookmarked - they should give you a good starting point: 1) http://www.simprojects.nl/toggle_to_momentary.htm 2) http://home.planet.nl/~schre010/fs/toggle.html
3) http://www.flightsim.com/vbfs/content.php?2178 4)
http://youtu.be/49gZlRIUer0 Also, my questions on Electronics.SE might help you.

There's got to be an electronics/programming forum that would be better for this.  I think this StackExchange would be helpful when you get the pieces and are trying to make the simulator more realistic, but as for knowing where to buy and how much things cost...  No idea.  Perhaps this could give you an indication? http://www.redbirdflightsimulations.com/

Start with: http://www.sportys.com/Pilotshop/category/2238
If you just want to buy a ready-made setup, look at http://www.sportys.com/Pilotshop/product/19371

If you could make the question a little less broad, it would be great!

@JayCarr You mean like Electronics.SE? ;)

@DannyBeckett certainly seems more suited in my mind...

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text:
Are used planes worth their money for a private pilot?
I am thinking about getting PPL as a base step for pilot career. But all my previous life experience tells me that without practice, any skills would decrease rapidly with time.
I have a sum of money not enough to pay for whole CPL training, but enough to pay for PPL training and to buy a used plane for a price, say, 30000$. I understand that that would be very old and primitive plane. But would this be a good investment if I wants to fly for increase my flight hours after training and do some activities, for example, to make money through flight blogging on YouTube?

It depends on way too many factors to be answered here. I think the better and much safer option would be to consult someone experienced and do your own research (better to trust yourself than someone on the internet).

Well, my question is the first step of such research.

not the best place...

Training is hard on engines, and it's a good idea to wait until you know you have a license before becoming an owner, so do your Private on a flying school's airplane so it gets beaten like a mule and not your pride and joy, then advertise for a partner or two to acquire something to build time in, and pool your money to find the best example you can, of an airplane that is easy to sell.
The used plane has the potential to be a money pit. On the other hand it's worth doing if you can spread the cost and get the right airplane. Buy a nicer one, like an old but really pristine C-150 or 172, with 1 or 2 partners, and create a micro-flying club. More than 2 partners, 3 owners total, the benefit of the cost dilution is not worth the hassles of "shared custody", but 1 or 2 partners works well for the right people.
With your fixed costs diluted by 1/2 or 2/3rds, the expenses that come up won't be anywhere near as painful. The financial pain from the maintenance/insurance/tie down or hangar bills kills the fun, so it's important to get the costs down to a level that doesn't bother you or force you to make major sacrifices in other areas and you can enjoy flying the hell out of the thing to build hours and go on to commercial.

How do you distribute costs among the 2 or 3 owners? In a fair and legally sound way.

@Michael I did the finances for a small 1 a/c club a number of years ago. We charged monthly dues to cover the fixed expenses. Aircraft loan, hangar, insurance, nav data base subscription and annual inspection all fall under this. Then you charge each member an hourly rate for using the a/c. The rate has to cover operating driven costs; fuel, oil, routine maintenance, and an engine reserve to pay for the overhaul ($15/hr will cover a $30k o/h at 2000 hrs.) At the time, it came to about $20k/yr total for about 200 flying hours-half fixed and half operating expenses (a/c was paid for.)

@Gerry I had a share in a syndicate with 3 C-180s on floats in the late 70s/early80s. 15 members were shareholders in a numbered company that owned the planes. and we rented them from the numbered company at a wet rate of around 38/hr. About 120/hr today. Plus a few grand a year as a share of insurance and docking etc.  About the cheapest way there was to accumulate float time. You mentioned overhaul: Plan for 2000hrs, but Savvy Aviation has a podcast where he talks about a micro club that got 5500 hours out of its O-360 before it was finally pulled for oil consumption.

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text:
How can I determine the fuel temperature in the tanks of an Airbus A320 during climb?
I know that, for example, at 10000ft the outer temperature is around $-10\, ^\circ\! C$.
How can I calculate the fuel temperature in the tanks?
In technical notes I find on the internet for Airbus there are mainly min max limitations that trigger the sensors.

without having the initial conditions and more info about the current situation, I don't see how you would calculate anything.

I was searching for some rough estimates or literature data. But unfortunately I do not have any other data to provide rather than the aircraft speed which is around 430 km per hour

While this is related to aviation, it is really more of a physics or math problem.  You might get a better response elsewhere.

The temp would be different if the fuel started at 30°C than if it started at 15°C, so you're going to have to come up with more parameters than you've provided.

And which tanks?  Presumably different tanks have a different surface area to volume ratios.  And why would you calculate when you can measure?  P.S. the time spent at 10K' is very transitory if you are climbing as the question indicates.  The OAT will be constantly decreasing.  Probably obvious, but it complicates the math...

@MichaelHall While frictional heating and cooling to ambient conditions can be calculated as a physics problem, you cannot use physics alone to determine the number one source of fuel heating: the engine fuel/oil heat exchangers.

Airbus has software to calculate this, called FTP, available to operators. If there's a legitimate need, you'll have to work with them, or find somebody at a carrier to run it for you.

To all commentators mentioning how complicated and variable: it is an engineering issue, with more than one input indeed. The answer can show the methodology, then set a start temperature as an example for a specific aeroplane. The question is about the methodology.

@MichaelHall we have an Aircraft-Physics tag.

@Koyovis - thx, added...

I understand the data provided are not much but as @Koyovis said I was mainly searching for a methodology to set an initial rough number and then work on it.

Maybe you can add the answer to another relevant question? "What is the fuel temperature in the tanks during a flight?" or I don't know how a question can be re opened

@sophit I have voted to reopen, but I am still not convinced. I'll wait to see your answer.

When a body at a certain temperature $T_i$ is blown upon by air at temperature $T_{air}$ there's an exchange of heat per second $\dot{Q}$ (in Watt) which is:
$\dot{Q}=hA(T_i -T_{air})$
where:

$A$ is the surface of the body involved in the heat exchange; and
$h$ is the convective heat transfer coefficient which tells us how good the flow of air is exchanging heat with the body; for example, moving air exchanges heat better than still air (think about a ventilator): in the former case $h$ is bigger; air blowing on the entire body's surface exchanges heat better than if it's blowing only on a small part of it: in the former case $h$ is bigger.

Now, when the body exchange some heat $Q$ with the surroundings, its temperature changes of:
$T_f-T_i=\frac{Q}{mc_p}$
where:

$m$ is the mass of the body; and
$c_p$ is the heat capacity which tells us how much conductive the body is; for example, air is less conductive than water: if you are invested from air at 200°C when you open your oven, it's not a big deal but just a couple of drops of water at some 80° will make you scream: air il less conductive than water and its $c_p$ is lower (1:4 more or less).

Now, if we equal these two equations and solve in respect of $T$ we get:
$T_f = T_{air} + (T_i-T_{air})e^{-bt}$
where:

$b=\frac{hA}{mc_p}$;
$t$ is time; and
$T_f$ is the final temperature of the body after $t$ seconds.

That's all!

Let's do the math for our kerosene flying at -50°C:

$h \rightarrow$ for a flat surface blown upon air at high speed, its value is some 100W/kgK;
$A \rightarrow$ let's suppose that the tanks occupies some 70% of the entire wing surface; for an A320 this makes $A=0.7 \times 124=85m²$;
$m \rightarrow 27'000l\times 0.8kg/l=21'000kg$;
$c_p \rightarrow$ for kerosene it is 2'200J/kgK;
$T_{air} \rightarrow -50°C=220K$;
$T_i \rightarrow$ this is the initial temperature of the kerosene, we suppose to takeoff on a sunny Sardinian day 30°C=300K;
$t \rightarrow$ let's see what happens after 1 hour of flight $t= 1 \times 3'600s$

Substituting:

$b=\frac{100 \times 85}{21'000 \times 2'200}=0,000184s^{-1}$
$T_f=220 + (300-220)e^{-0.000184 \times 3'600}= 220 + 41= 261K=-13°C$

So, after having been blown upon with air at -50°C for one hour, our kerosene has gone from +30 to -13°C.

We introduced some simplification:

we have supposed that the whole mass of kerosene interacts with the -50°C of the air; obviously only the layers of kerosene on the surface exchange heat, the innermost part is not in direct contact with the -50°C and it doesn't change its temperature so fast as the outer layers;
kerosene is used as coolant in the various heat exchangers which can be found on a jetliner; this heat exchange raises its temperature and has to be taken into account.

Anyway as a first conservative estimation that equation should be enough.

+1 for explaining the underlying physics! However, a temperature change of 43°C in one hour seems rather excessive to me. If you look at the plots in Airbus FAST 36 (PDF, page 8), you'll see temperature changes of 20 to 30°C (depending on which tank) during the first 1000 NM of the flight (about 2 hours).

@Bianfable: thanks  As said at the end of the answer, this is a conservative estimation, the real value is going to be less (drop of temperature) as you actually shown. Anyway note that the plots from the pdf use 5° as initial temperature and -60°C for outside air temperature. And from the picture of the wing my 70% seems to be a bit too high. I try to redo the math with the values of that plot, thanks for sharing it

I think this is the opposite of a conservative estimate. This gives a sort of upper bound, and a conservative estimate usually gives a lower bound.

@Federico: well "conservative" means "closer to (or even past) the worst case". Here the worst case is frozen fuel, which is the exactly the direction given by the calculation (-43°C temperature drop instead of some -30°C as per plot provided by Bianfable). So, the calculation has simplifications but they are conservative.

Math is interesting and fun to follow.  Since both top and bottom of wing exchange heat, A value might be 2x.  Also, a crude volume to surface area ratio might bring these "ball park" numbers even closer. +1.

@RobertDiGiovanni thanks. I also thought about the x2 but then I thought that actually only the fuel on the bottom is directly in contact with the -50°C.

Oh, could it be this is the thermodynamic version of mass v drag area.

Good explanation! my first thought was .. oh that leads to some ODE.. and you elegantly just presented the solution :)  I think it would be worth writing the ODE and at least state that how it can be solved. Fortunately in this case it's fairly simple. My cheeky side was going to suggest "fuel consumption" to make it mathematically a bit more interesting, the next step would be also varying external temperature from take-off to cruise altitude. For long flights your example numbers show that numbers would stay in the same ballpark,but what is the temperature 10min after takeoff?

@CarlBerger: thanks I just wanted to show the general process without going into detail.

The fuel temperatures in the wing fuel tanks are displayed to the pilots on the ECAM (electronic centralized aircraft monitor) FUEL page below the fuel quantity indications. Pilots can select this page manually and the ECAM can also call up this page automatically if fuel temperature gets too low.
You can see the fuel temperature indications in this video:

The actual fuel temperature inside the fuel tanks depends on the static and total air temperatures (TAT), the fill level of the tank and other major factors. For example: The fuel is also heated by the engine oil heat exchanger. Flying faster can increase the TAT and heat up the wing surfaces and the fuel inside the wings by heat exchange processes (as others already have shown in their replies). But also increasing the airspeed increases the drag of the aircraft so you need a higher engine thrust to keep the high airspeed. Higher thrust requires a higher engine RPM, increasing engine oil temperature over time. And because of the engine oil heat the with fuel that is going back to the fuel tanks is heated whist the engine oil is cooled.
So on an almost empty tank, during the descent with the engine at idle and at high altitude after a hours of flying in cold air the fuel is very likely going to reach the coldest temperature in the fight. Sometimes it can remain cold enough so that during the descent or even after landing ice can form on the upper and lower surface of the wing, known as cold soak effect.
Here is an example of the cold soak effect:
https://www.airliners.net/photo/Air-Canada/Airbus-A320-211/991791/L


text:
Fighter aircraft information
Can fighter aircraft accomodate more than one pilot who flys the plane?
I mean similar to pilot, copilot.
In general if Yes or No, Is it useful to have more than one pilot in a fighter plane?

Prashant Akerkar, you are asking a very basic question again, which isn't received well by the community. The most important thing missing from you questions is research effort. Linking a Wikipedia article or a Google search is not research effort. You should try to find an answer or at least gain some understanding first, and then come back here and ask specific questions about the things that are still unclear.

This has been explained to you before under this question on Electronics.SE. It also doesn't help that you have been blocked on other sites because you are accused of trolling. Please show more research effort before asking.

Sometimes.
Some fighters were designed with two seats from the start, such as the F-4 and the F-14. These planes had complicated radar systems and they needed a specialist operator. While flying them, pilots have found that having a person in the back seat who can look out for enemy fighters is very handy.
Most single seat fighters, such as the F-15 and F-16 have double seat versions. These double seat versions are used for training and for bombing. For instance, the basic F-15A has a single seat. The F-15B has two seats and is mostly used for training. The F-15C is an upgraded version of the F-15A and still has one seat. The F-15D is an upgraded version of the F-15B and still has two seats. The F-15E is an all-weather strike aircraft with two seats.
In most two-seat fighters, the pilots sit one in front of the other. In some, such as the F-111, the crew sit side by side. Putting the crew one in front of the other allows the plane to have a smaller, lighter body, but the person at the back has a very bad view forwards this way.
As a general rule of thumb, smaller, lighter fighters tend to have one seat and larger, heavier ones have two.

The second person in the F-14, F-15E, and F-111 isn't a pilot but a WSO (Weapons System Officer) or RIO (Radar Intercept Officer) - not a pilot but a navigator (Air Force) or Naval Flight Officer (Navy - same thing, different title). In the F-15 and F-16 B and D models, the second person typically would be a second pilot, either in student/instructor roles, or for a checkride. Though those aircraft can be flown single-pilot solo, or with an observer in the back seat.


text:
What's this hole on the ATR-72?
There is a hole on the belly fairing circled in yellow. I guess is an air intake but I tried searching some info and couldn't find anything.

Source

By the way, this kind of hole isn't restricted to the ATR-72; the 737 also have a similar design feature, and it is for the same purpose as well.

It is the ram air intake for the air conditioning system. There are two of them, one on each side.
Here is an image from the ATR-72 FCOM:

ATR-72 Air conditioning System, image from 737ng.co.uk
Details from the same document:

The air conditioning system is supplied by air processed through two packs which regulate air flow and temperature. The two packs are installed in the main landing gear fairings and operate automatically and independently.
The left pack supplies the cabin and cockpit air conditioned; the right pack supplies only the cabin air conditioned.

Also, as @Jonathan Walters points out, the intake is a good example of NACA inlet (or NACA scoop) and are found in a number of aircraft, for example Boeing 737.

You might consider adding that it is an example of a "NACA scoop"

A ram air inlet for reducing the heat of the Primary and Secondary Heat Exhangers caused by the bleed air coming from the PACK Valve (Primary XCGR) and from ACM Compressor part (Secondary XCGR). It is usually ventilated by 2 means:

RAM AIR if the speed is > 150kts or
Ground cooling turbofan (operated by bleed air coming from Pneumatic system) if the speed is < 150 kts.

This ram air is exhausted outboard via a ram air outlet near the Main Landing Gears

Note: The operation of the Ground cooling turbofan is electrically controlled by MFC and pneumatically operated by bleed air from pneumatic source (ENGINE).

Hope this helps..
B.E. Nolasco
ATR 72-500 Maintenance Instructor


text:
What are these grilles in the passenger cabin of this 787?
Below the windows, ahead of the seat, there are small grilles. Look:

Source: Airliners.net
What are those for?

The answers to this question indicate that these are the exhaust vents for the cabin air circulation. I think they appear to be much too large for just that purpose. I don't have a technical reference for this, but I believe those vents also prevent the cabin floor buckling in the event of a sudden pressurization failure.
The cargo hold is beneath the passenger cabin, and both are pressurized because the cylindrical hull can resist pressure better than the flat cabin floor. If the cabin suddenly loses pressure the air in the hold could buckle the floor upward, or if the hold loses pressure the air in the cabin could buckle the floor downward. The floor must be generously vented to prevent this.
US patents # 6129312 and # 5137231 claim systems for combining the cabin air circulation vents with the depressurization relief vents. From the '9312 patent:

An air return grille mounted below the passenger cabin sidewall
  comprises openings to allow return airflow from the air conditioning
  system. The grille openings are covered by a single thin baffle with
  cutouts within its periphery that slip over and are held in place by
  fasteners on the molded grille. During normal operation, the thin
  baffle restricts flow through a small opening in the grille. During a
  sudden decompression of the cargo compartment, the baffle is dislodged
  from the fasteners. This allows the airflow to pass through all of the
  molded grille openings in order to achieve rapid pressure
  equalization.

The panels are usually referred to as "dado panels". As an example of what happens when an explosive decompression is too violent for the dado panels to equalise the pressure (and protect the floor structure), see AA Flight 96.

@Lightsider will that blow away passengers legs?

In short: They are special air paths named the dado panels or decompression panels:

In normal conditions they are partially open to allow air entering the cabin from the ceiling (crown) to exit into the cargo holds.

In case of rapid decompression from a hole in the cargo holds, they fully open to accelerate pressure equalization between the two levels and prevent the cabin floor to collapse down under the effects of high pressure differential.

They are standard safety equipment since a NTSB recommendation after a DC-10 explosive decompression in 1972, due to a cargo door opening in flight. The cabin floor collapsed:

disrupting various control cables which were routed through the floor
beams to the rear engine and to the empennage control systems

In the principle they are similar to the louver panels found in restroom doors (doors may be undercut instead). They play a secondary role as firewalls.

In the architecture lingo, the dado is the lower part of a wall below the dado rail. The grille portion of a passenger aircraft wall is called the dado module. It consists on a louvered air grille over a decompression panel (sometimes called the dado panel) which can be open or closed.

Boeing patent for a decompression panel, source
The cargo compartments on a pressurized aircraft are not always fully heated, but they are always pressurized, being part of a single pressure vessel (a cylinder sealed by two bulkheads).
Air from the packs (conditioning system) enters the cabin usually from the ceiling and leaves it by the dado modules, e.g. (A320):

Cabin air distribution, source Airbus

Longitudinal flow, schematic principle, source
There are recirculation ducts in the cargo section with fans drawing air from the cabin. Air is then reconditioned and sent back to the cabin. A fraction is dumped overboard though the outflow valves to regulate pressure in the aircraft.
In case of decompression
In case of rapid decompression in a cargo area, there is a risk of cabin floor collapsing due to the pressure difference above and below it. This happened in 1972, as @krmezljavKuza mentioned. The related NTSB investigation report included this recommendation:

Require the installation of relief vents between the cabin and aft
cargo compartment to minimize the pressure loading on the cabin
flooring in the event of sudden depressurization of the cargo
compartment.

The decompression panels open to act as pressure relief vents and allow a larger quantity of air to flow into the cargo compartment. Pressure can equalize before the floor is damaged.
There are similar decompression panels in the triangle areas indicated in the picture above, between the different sections of the cargo level. There are also louvers in various panels, e.g. lavatory doors.

TIL "dado rail" = "chair rail". I'd only ever heard the latter term. Thanks for the additional education.

This answer was quite informative.

The grilles are almost certainly meant to equalize pressure between the cabin and cargo bay, particularly in case of rapid decompression. As far as I know, the design feature stems from two consecutive accidents with the DC-10, American Airlines 96 on 12 June 1972, and Turkish Airlines 981 on 3 March 1974. Though the cause of both of these decompressions was a poorly-designed (and poorly-maintained) cargo door, in both cases, the real damage was caused by the collapse of the cabin floor, which  severed control cables, and on Turkish Airlines, broke hydraulic lines. After these accidents, the grilles were added to equalize pressure and prevent the floor from collapsing. The floor itself was also strengthened.
If I remember correctly, one of these accidents was the subject of an episode of Air Crash Investigation.

Air Crash Investigation S7E1 "Shattered in seconds" about China Airlines flight 611 on 2002-05-25 (decompression due to fuselage rupture caused by a faulty repair after a tail strike on 1980-02-07) mentions dado panels and an accident with a Turkish Airlines flight in 1974 (together with reconstruction footage of that accident), and it is said that the Turkish Airlines accident led to a NTSB recommendation about adding more dado panels to the cabin. All of this is in sum a good indication that there also is an episode about that particular crash.


text:
What is this hatch above the cockpit of a 747?
There is a little door on the upper deck above the cockpit:

Source: Airliners.net, (modified to indicate location of hatch).
What is that door? What is its purpose?

It's an emergency escape hatch. There are inertial reels in the cockpit ceiling adjacent to the hatch to allow the cockpit crew to exit the airplane. See this link for an account of their use escaping the aircraft during a hijacking.
There were five reels in the 747-100/200 aircraft. The cockpit had five seats: pilot, co-pilot, flight engineer, and two observer seats.
It's also sometimes used in third world countries to send a guy out to clean the cockpit windshield. In Mumbai I once made the mistake of asking the windshield to be cleaned, thinking, of course, they'd do it with a cherry picker. Much to my surprise, bare feet appeared at the top of the windshield followed by this poor fellow who was maneuvering into place to clean the windshield. He had a rope tied around his waist, but had he fallen it would have been bad because the rope was anchored through the hatch, which meant he would have swung badly had he fallen.

Nitpick: the aircraft in the picture is a 747-400 and has a cockpit crew of two, not three.  The article you linked is 30 years old and describes a 747-100.

@NateEldredge Whislt the minimum cockpit crew for a 747-400 is two, it is very common to have three people on longer flights. Even on shorter flights KLM often has a junior "co-co-pilot" on the 747.

Or a instructor on a checkflight

https://www.youtube.com/watch?v=2y5lNVbBeiU

@Terry - any thoughts why they used an overhead hatch on the 747 instead of the sliding window as in smaller Boeings?

@RalphJ I don't know why they went to the overhead hatch instead of the sliding windows. The only thing I can think of is that having decided to use inertial reels instead of the simple strap (as I remember at least) for the windows, they lacked room adjacent to the windows for the inertial reel storage. I came to the 747 from the 727, which had the sliding windows. I remember thinking I'd miss being able to open the window, but I didn't.

It took me several minutes of horrified contemplation before I realized that this hatch was only meant to be used while the plane was not in motion.

@Crashworks: This whole thing reminds me of those heart-stopping videos on YouTube featuring idiots changing the tyres on a car while it's being driven.

@Terry, just curious how your first notice of the windshield washer would have been his bare feet on the window. Wouldn't you notice people in the cockpit, opening the hatch and crawling out? Is the hatch access not directly in the cockpit?

@FreeMan This was a freighter sitting on the cargo ramp at Mumbai, then called Bombay. Freighters had the cockpit door removed so the cockpit and the upper deck were one area. Behind me there was typically lots of activity what with the loadmaster and ground personnel finalizing paperwork. Also, it was not uncommon for the f.e. to open the escape hatch, which was basically opposite him, to get more airflow. This guy backed down over the windshield from the top, so the first I saw of him was the bottoms of his bare feet at the top of the windshield. It was a different world back then.

@Terry - got it. That makes a lot more sense now. And thanks again for sharing your stories - they're great!

@Porcupine911: And I was trying to explain why they'd have a guy crawl out that hatch with a squeegee, even though the plane has wipers.  (Probably, anyway - I've never owned a 747, so I have no first-hand knowedge :-))

@jamesqf 747-100/200s do have wipers, but they're not like car wipers that have a squirt and clean function. All they do is wipe, and as I remember there was a prohibition against use on a dry windshield. The only times I ever used them was in extremely heavy precipitation on short final. Most of time, actually almost all of the time, the airflow over the windshield was more than sufficient for precipitation removal. In ten years on the 747, I think I used the wipers less then ten times.

@RedGrittyBrick: That is some very upbeat music for a video showing how to evacuate an aircraft's flightcrew in an emergency.


text:
What are the wings and fuselage of an airliner made of?
Which materials are used to make the wings and the fuselage of an airliner, for example the Boeing 767 or the Airbus A320?

this risks being a tad broad, all possible steel/aluminium/titanium alloys + fiber composites are quite a lot. But I concede that only a finite list is used for the fuselage/wings. Let's see what the answers bring, but if you could think of a way to narrow it down a bit, I think it might help.

Most modern planes are made mostly of aircraft aluminum. Or at least are skinned in aluminum. The spars and cross members may be made of other materials but I am under the impression they are mainly aluminum as well. Generally high stress areas like wing/fuselage joints may be made of more rigid materials like steel. Aircraft Spruce provides a nice break down of the various types of aluminum here. This answer to a similar question provides a nice break down.
As the technology gets better and the facilities grow in both scale and ability, composites like carbon fiber have found their place in planes like the 787. Here is a break down for the 787

(source)

The "source" link would be more useful if it pointed to the document where the image is embedded rather than being just a link to the bare gif.


text:
Can a handgun shot take down a commercial airliner?
Most airplanes, when taking off or landing, are in range of small arms fire, i.e. your every day handgun.
Is it possible to take down a commercial airliner by shooting at it with a handgun? Would one shot be enough, or would several be needed?

This may be a bit broad. The weakest link is probably the pilots, and it doesn't even require a gun.

My question isn't, "what's the easiest way to take down an airliner". It's quite specific.

I would imagine the answer must be 'yes'.  Aircraft have been shot down with rifles after all.

Interesting read, however not a modern commercial airline.

This might be theoretically possible if you got a really, really lucky shot, but it's incredibly unlikely. Nearly everything critical to flight safety (including the flight crew!) is redundant in a modern airliner with many of the systems being triply redundant. For a single shot to take one down would be incredibly lucky (or unlucky, depending on your point of view.) Even emptying a mag into one seems extremely unlikely to actually take it down. Consider that modern airliners have had engines violently explode without even any injuries.

@SteveV.: Interesting link, but poorly researched. When the Italians attacked the Turks in Lybia in 1913, the Turkish side hired French pilots with their planes to fight the Italians. It was then when the first shots between planes were fired, and aerial victories scored.

I vote to reopen the question, while the answers may vary, it is quite possible to provide an academic answer.

Related: Accident: PIA A313 at Peshawar on Jun 24th 2014, aircraft under gun fire on final approach. It was a bigger gun and multiple shots, but while it managed to kill one and injure another two persons on board, it didn't do much damage to the aircraft itself.

"your everyday handgun" - Welcome to America, y'all.

shooting at it with a handgun

That's really going to depend on the handgun.
James Bond carries a Walther PPK - this is a .32 calibre popgun with rather limited use outside of a small office. Direct hits on people are usually survivable unless you take a round in the heart or brain. Chances of even hitting an airliner during takeoff or approach are zero - it simply doesn't have the range, and that tiny subsonic projectile will get deflected by the aircraft's wake.
Skipping the middle range and going straight for the hand-cannons, we might get somewhere with a Desert Eagle or a Smith & Wesson 500. Remember the posters for the first Terminator movie? The one where The Ah-nuld is wearing sunglasses and holding up some light artillery? These are bigger. At close range, both guns can crack an aluminum engine block1 and are one-shot kills on most things smaller than a rhino. Hitting an approaching widebody isn't all that difficult - it's coming toward you, the angle isn't changing, and it's a rather big target.
But aircraft are large, complex systems with a lot of redundancy, so in order to actually take it down we have to hit something critical. Hitting a 767 right in the nose will destroy the weather radar and (maybe, if it has enough energy left) poke a 1/2 inch hole in the forward bulkhead. No one will notice. The flight-deck windows are rather strong, apparently a police sniper tried to take out a hijacker on the flight deck way back in the 1970s and the rifle round (far more powerful) just pock-marked the window. Several hostages were promptly shot as a result.
The best shot (ha!) is the engines. They don't like ingesting bits of metal but just hitting the fan won't do much. You would have to get very lucky to get the round into the engine itself, where it will promptly do a lot of very expensive damage.
But even if one engine literally goes boom it still won't crash the plane. Pilots practice for an engine failure on takeoff all the time, and an engine failure on landing is almost a non-event.
Hydraulic lines for control surfaces are certainly sensitive, but they are well buried in the structure and there are several independent systems. You won't get them all.
So, in conclusion, handguns are sufficiently ineffective at bringing down large aircraft that we really don't need to be concerned about them. There's a reason air forces around the world prefer missiles or 20mm cannon2 for this sort of thing. Geese, however, are quite effective if released in sufficient numbers along the takeoff path. Rather noisy though - you won't hide 500 of them anywhere near an airport without someone noticing.

Internet legends of a .50 cal being able to kill a truck refer to the MUCH larger .50 BMG round, available in explosive and armour-piercing and rightfully categorized as a first-class military weapon.
The projectile's the size of your thumb, and the gun fires 6,000 rounds per minute. It'll do your plane like a chainsaw.

The Walther PPK projectile gets deflected by the aircraft's wake? Come on! Check your facts!

It's tiny - 5 grams. And it's subsonic leaving the barrel. I don't mean it's going to bounce off like the Enterprise's deflector shield but it will drift off target a lot more than heavier rounds. A decent crosswind can move a rifle round meters off target and they have a lot more energy. You need mass and energy here, and a .32ACP lacks both.

The wake is behind the aircraft. If the wake had any effect, the shooters aim would be far off target. Besides, it would only affect a small portion of the projectile's path. Crosswind works for the full length, that is why it makes such a difference.

Alright, lets forget the widebody-class wake for a minute. If you are shooting at me from ~200 meters away with a .32ACP I am going to stay right where I am: the aiming point is the least likely place you will hit. I will laugh and make disparaging comments about your marksmanship. Take out one of the other two and I will be leaving at Usain Bolt speeds.

I imagine if you shot a blade and it spit the blade into the compressor that the results would be pretty devastating.  If sparrows can take out engines...  You'd still, of course, be left with an operable engine and be fully capable of landing the airplane.

@RhinoDriver maybe. But the aircraft can get lucky too. During flight testing of the F/A-18 prototype the pilot noticed a weird vibration in one of the engines and decided to land and investigate. Turned out one of the front fan blades was missing. There was some damage inside the engine suggesting it had gone all the way through, but the engine still more or less functioned (it was replaced).

FWIW, in my imagination a shot to take down a commercial airliner would come from a position in front of the plane, in other words the plane would be making it's takeoff run towards me. I think that would eliminate wake turbulence.

It should be noted that there is at least one .50 BMG handgun.

It depends where the shot is fired and what counts as "taking down".
If you fire a handgun inside the cabin during a regular flight, the pilot will likely divert to the next airport and land. The aircraft is "down", but probably not in the way you were thinking of.
If you fire at the plane from the outside, in most cases the result will only be detected at the next bigger inspection. If you are "lucky" and hit something important, a system might fail and the airplane is marked for repair after landing. But it will not go down in flames.
For the way the question was probably intended to be asked, my answer is No.

There's one way it will bring the plane down: shoot one, or especially both, of the pilots.

@raptortech97: To kill both pilots with a single handgun shot from the outside during takeoff or landing (as the question implies) is in the range of will-I-be-struck-by-a-comet likely.

You're totally right. For a while there I completely forgot how inaccurate handguns are (and how accurate one would have to be).

As I remember, at the first 747 carrier I worked for, a few bullet holes were found in the vertical stabilizer of one of the aircraft, a freighter, when it was undergoing routine maintenance. The aircraft had been through Mogadishu some weeks earlier, and that was felt to be the best candidate as to when it had happened.

How about a shot at the fuel tank area? Would that just cause a leak?

@Sandy: Yes. Nothing more. The tanks are filled with kerosene, which is hard to ignite, and what is not filled with fuel is taken up by an oxygen-reduced inert gas which prevents combustion. The tank would just pee a thin stream of fuel. In an extreme scenario, the aircraft has just braked hard, then taken off, and the fuel pees on the red-glowing wheel brakes. Now the plane would trail a small flame, but this would still not be enough to ignite the fuel in the tanks. Real life ≠ Hollywood.

@raptortech97 not just (or not so much) accurate as powerful. Handguns lack the range and penetrating power to reach an aircraft during takeoff or landing (from a position outside the airport runway system), penetrate the cockpit walls or windows, go through even one of the flight crew (let alone both), and leave a hole in them big enough to be fatal.

It depends on who shoot the plane.
With the spirit of Juche idea, Kim Il Sung (Supreme leader of North Korea) can shoot planes with handgun easily. There is a selection from North Korea textbook:)

General Kim Il Sung left the cave and saw several of the bombers from US imperialists bombarding the base continuously. The heroic People's Army soldiers kept shooting the American aircrafts but useless.
Frowning angrily , the General saw an American aircraft tried to bomb again, he raised his handgun and aimed at the enemy aircraft. When the enemy is aligned the people army again and came down, the General shot. Shortly, a mass of huge fireball erupted in the sky with falling wreckage. The remaining US pilots were scared and escaped. Soldiers cheered toward the General Kim Il Sung:
Long live the Great Leader Kim Il Sung!
Long live the Great General Kim Il Sung!

But for other people, it seems impossible. Major damage of shooting comes from explosive within warhead. In WWII, most of the fighters installed 20mm machine gun or even larger, however, there is many case which the heavily shooted fighters have successfully landed on runways and aircraft carriers. Handgun even cannot kill a man for some times, how can it shot down a plane by most people?

Good example to put into perspective, thanks.

can even imagine that working, sorta. If you get lucky when shooting at a B-29 carrying a load of incendiary bombs (which are very thin walled containers filled with white phosphorous in those days) you may well set off a chain reaction resulting in said fireball. Unlikely to do with a pistol at the range they'd be, but turn a high power scoped rifle into a pistol for artistic license...

Omg someone trusts that is true

Small arms fire absolutely can take down aircraft: http://www.lonesentry.com/articles/defga/ (WW2)

In one instance in Africa, an eye-witness reported the destruction of three Italian planes in 5 minutes by small-arms fire. In another case, the Germans claim to have brought down a Soviet plane with an automatic pistol.

United States Army Air Defense Artillery School "Small Arms Defense" describes tactical doctrine: saturate the region in front of the plane aircraft with lead and hope that enough hits are made to critically damage it.

Your first example is from WWII, not exactly comparable to modern commercial airliners.

Small arms in this context means assault rifles and light machine guns and backpacks full of ammunition. Quite a bit bigger than what normal people call a “handgun”.

This when I got to give “the lawyers answer“ to:  Well, it depends...
It depends on the kind of gun that you use, where are you hit the airplane, and how much energy the bullet has at impact.
My basic answer would be that it’s very unlikely you could do this.
Some basics: handguns are notoriously inaccurate and under powered -  some firearms instructors go so far as to say the only purpose for a handgun is the fight your way back to a long gun.  The main purpose for such a firearm is as a compact means of self protection at close ranges and they were never intended for anti material use.  A typical handgun in the hands of an average shooter has an effective range of about 50-100 yards and packs about 300-700 Ft-Lbf of muzzle energy with poor ballistics (~1000 FPS, depending on model).  Larger handguns do pack a bit more energy (~1400 FPS and ~1500 Ft-lbf at the muzzle) but the application still remains the same.  This rules out the use of a gun against an airplane for anything but at point-blank range i.e. a guy hanging out at the fenceline of an airport taking a potshot at a 737 waiting to take off probably is either not going to hit it at all or with such poor accuracy that it can’t hit a vital system which could disable the airplane. Given the low muzzle energy of handguns, it’s unlikely that the round could penetrate critical components such as either the engines or the APU and disable them.   There is a chance though that’s such a round could penetrate the cabin of an aircraft and injure or kill a passenger.
As to whether a person could shoot an airplane flying overhead with a handgun, my response is no.  Airplanes are notoriously difficult to hit with firearms in flight and dedicated anti-aircraft systems will either utilize radar guided automatic weapons of a much more powerful round than a handgun uses, or large quantities of ballistic artillery shells fitted with proximity fuses and blast/fragmentation warheads to saturate an area where the aircraft is.   A single person with a handgun has virtually no chance of hitting an airplane like that.

If the bullet is able to damage a tire, such that chunks of the tire fly off, those chunks could cause even more damage than just the bullet alone.  That was enough to bring down a Concorde (Flight 4590).

A handgun is very unlikely to shred an aircraft tyre, some may not even be able to cause a puncture. Even then, the Air France Concorde wasn't brought down directly by the damage but by a chain of unlikely events: the fuel leak was ignited by the afterburners (which most airliners don't have). The fire cause an engine alarm, and the (still functioning) engine was shut down, and the (overloaded) plane was unable to maintain flying speed on three engines. (Source: Aircrew Interview video)

If the round from the handgun penetrated the partially-filled fuel tank of the aircraft, the ullage area would likely have a fuel vapour and air mixture and be prone to explosion leading to the separation of part of the wing from the aircraft. Large numbers of combat losses are attributed to this phenomenon before the introduction of either mechanical or chemical methods of preventing this fuel-air mixture from accumulating in the tanks of combat aircraft even as recently as the mid 2000s.  Since this adds weight and potentially reduces available fuel capacity I don't believe this is included in civilian airliners.
So the answer to your question is yes.  If the aircraft were on short finals or just departing then your handgun round could possibly take down an airliner.

If it pokes a hole, the pressure in the cabin will be lost (which involve possible injury to the ear drums or death of the people inside, as at cruise altitude there is not enough oxygen in the air for the human body, which is why it is pressurized inside and maintained at near sea level pressure).
The aircraft can be damaged to the point of losing a structural panel, but not necessarily crashing. Unless the pilot falls unconscious due to the lack of oxygen. (Oxygen mask only have about 15 minute of oxygen by the way).
If the bullet hits an engine, or poke the wing (i.e. fuel tank), then there is high risk of explosion, with dramatic consequences.

you are near ground already, no depressurization will happen.
also, explosions happen in films, hardly in real life.

Even if you are at altitude and suffer depressurization, 15 minutes is plenty enough to get down to a reasonably safe altitude even from jetliner cruise height. Even a normal landing descent is on the order of 2000-2500 feet per minute and that gets you from jetliner cruising altitude (30,000 feet) to ground level well within those 15 minutes. Also, even assuming the bullet penetrates the plane (see other answers), a handgun would punch a relatively tiny hole; it's not like that is going to cause instantaneous decompression.

It probably wouldn't cause significant decompression at all. The hole would be so small that you could just stick one of the in-flight magazines or something up against it and stop the leak completely (and this is assuming the plane is pressurized, which it probably wouldn't be.) Even if the plane were pressurized and no one bothered to plug the hole, the hole would be so small than the outflow would most likely be less than is already happening intentionally through the aircraft's outflow valve. And explosion will absolutely not happen. Jet fuel isn't explosive at normal pressure/temperature.

The cabin outflow valve would close a little in response to the cabin altitude change and they probably not find the hole for quite some time.  A few flights at least.


text:
How does a Missile Lock Work?
When we say that a missile has been locked on a target (lets assume a fast moving target, and that the missile is mounted on a fast moving plane), we assume that once the missile has been locked onto the target, it will actually hit the target after firing (Irrespective of the subsequent changes in the position, velocity and acceleration of the target). How does this system work?

I was just reviewing some of your Wiki edits. Please make sure both the tag excerpt and the body read as stand alone text. I've seen that you use the excerpt as an introduction and then use the body to give examples. When only the body text is presented to a user all context is lost. Unfortunately I had to vote to reject several times which feels like I am wasting your efforts and I don't like to discourage people from writing wiki entries.

Fair enough. I'd look into that. Thanks :)

"will hit the target" is an overstatement. It will try.

Read This the best possible answer to this question.

Missiles use advanced algorithms to predict the best path to intercept the target. The seeker-head in the missile will be looking at the target (either IR, reflected radar energy, or using it's own radar depending on the missile type) and attempt to guide itself to the predicted intercept point, in order to have the shortest possible distance to cover. It basically flies towards an intercept point ahead of the target aircraft. When the target aircraft direction changes, so does this predicted intercept point, and the missile manoeuvres to fly towards the new intercept point. this is of course a continuous event.
Furthermore missiles usually have multiple stages of guidance. In the beginning they will fly just in the general direction in order to save energy, and only in the later stages will it start manoeuvring to the intercept point.


text:
What is the cost savings of using electronic motors to taxi?
Aircraft manufacturers are now planning to use High Torque electric motors on the nose wheel of the aircraft, which is powered from the APU, to taxi the aircraft from the gate to the runway without using its main engines. This is intended to reduce the fuel consumption by the plane while being taxied using the main engines, but also adds additional 150 kgs approximately to the weight of the aircraft.
How much fuel savings are we talking about here? Lets say we are considering an A320?

There is some information here: http://www.greentaxiing.com/benefits.html
It's a biased source, so it's not an ideal answer, but it may be a place to start.
This specific system, btw, is installed on the main landing gear. It looks like this: https://upload.wikimedia.org/wikipedia/commons/0/05/Safran_Honeywell_EGTS_Airbus_A320-212_F-HGNT_PAS_2013_01.jpg

Sounds messy to me.  Extra APU output required and, if it's not a busy day and you get a rapid ATC/takeoff clearance, you would incur delays while holding short or on runway as you struggle to get the main engines started and complete your checklist:(

There are additional advantages to just fuel savings. Taxiing backwards and pushback without a tug, and, when this option starts to see widespread use, improved safety for ground crews, because the engines could be started much later, during taxiing, well away from the gate/apron.

Electrical taxi propulsion, air-conditioning or bleed air for starting.  Pick any one:(

@MartinJames you don't necessarily need to be rolling while starting the engines.  And you can momentarily suspend the air conditioning.  Delays tend to be predictable minutes in advance.  Though if an engine ever fails to start that could mess up the choreography.  Even without this, I've been on flights that shut down some of their engines while parked in an hour-long line on a taxiway.

Jet engines are not very efficient at low power and speeds, so using an alternative method of propulsion is a good opportunity to save fuel.
An aircraft the size of an A320 will probably burn about 200 kg of fuel during taxi (based on this and this). Assuming fuel costs \$3 per gallon, this is about \$200 per flight.
The cost of the added weight from the electric motor will vary based on flight length, but assuming \$0.05 per pound, the extra cost would be \$16.50. Of course you are saving 200 kg of fuel, so this also helps to offset the weight. The electric motor is powered by the APU which uses much less fuel than the engines.
As KeithS points out, this adds up quickly. Even if United Airlines only equips its 150 A320 series planes with this equipment (which would certainly be a large upfront cost), and those planes make 5 flights each per day, that adds up to \$150,000 in savings every day. This will of course depend on fuel prices, which are actually well under $3/gal at the moment.
A simple way to save some fuel while taxiing is to only use 1 engine (or 2, for four engine planes) to taxi. This doesn't save as much fuel as the electric option, but also has much less upfront cost.

$200 may not sound like much, but that's only one plane. There are about 93,000 scheduled flights per day, and a few times that number has exceeded 100,000, so overall this would, if fooot's figure is correct, save the airline industry an average of  $18,6 million daily. In addition, while airlines get bulk discounts and hedge fuel price increases with futures, the spot price for Jet A in the DFW area yesterday averaged $4.80 a gallon, a 60% increase over fooot's quote, which increases the potential savings proportionally.

Interesting that the 2nd of your taxi fuel burn links shows 100Kg of fuel burned on the way out, yet only 50Kg burned after landing. I guess the fuel burned in-flight makes the post-landing plane lighter for taxi?

@FreeMan Maybe partially, but I think it's more likely to wait in line for takeoff than to wait for a gate. Depends on the airport of course.

That makes sense.

What about the overtimes that the APU will do from the gate to the runway? The extra working hours will bring APU much closer to its next maintenance. Or the APU maintenance cost is trivial compared to the fuel saved?

@SteliosAdamantidis APU loading worries me too, especially if it is expected to start the main engines while also taxiing and trying to keep the lights on.

There are savings beyond just fuel when using a electric taxi motor on a commercial aircraft. Your title seems to ask about this but the text asks only about fuel. WheelTug, a developer of an electric taxi system, answers both in a pretty thorough presentation.
Direct cost savings per flight is about 210 dollars, most of which is avoidance of pushback tug cost. Only about 80 dollars is taxi fuel, which then has to be reduced by 10 dollars per flight in "tankering", the extra fuel burned to carry the 300lb of electric motors throughout the flight. Net fuel savings is 70 dollars per flight.

Much larger savings accrue indirectly through time savings. This includes financing cost of aircraft, increased utilization, reduced injury and damage, avoidance of cost due to delay and the like. It puts this number at about 550 dollars per flight. This makes the total savings 700 dollars per flight, according to WheelTug.


text:
What special tyres (tires) are needed for high altitude takeoff and landing?
I just watched this video of AA922 taking off from El Alto (LPB) to Santa Cruz.  The video's author mentions that the aircraft needs "... special tyres" due to the high altitude.
While I do understand the physics and aeronautics associated with high altitude takeoffs (extra ground speed; longer runway needed, etc.), I'm curious:

What specific modifications to the tires (special or synthetic rubber, extra tread, stiffer sidewalls, etc.) are needed for high-altitude ground operations?
Should I assume these tires are the exception, not the norm, because of economics / higher prices / more maintenance?

The higher takeoff speeds might exceed the speed rating of the usual tires. As a tire is rolling it deforms in two directions.

As each section comes in contact with the runway it is pressed inward by the weight of the plane. After it leaves the runway surface the deformation is in the opposite direction from centrifugal force. This constant flexing is what causes the tires to fatigue and possibly fail. The flexing also causes heat to build up in the rubber which causes the rubber to lose its flexibility.
The faster the tire spins the more centrifugal flexing occurs and the shorter the period between force reversals. This shortens the time the tire has to dissipate heat.
The two ways to increase speed rating of a tire is to reduce the flexing and to reduce heat retention. The way manufacturers reduce flexing is to add cap plies. These are usually of nylon or other synthetic material placed on top of the body plies on axial ply tires and on top of the steel belts on radial tires. These help keep the body plies from deforming outward from centrifugal force. The faster the tire must spin the more cap plies are used.
To reduce heat retention the rubber used between plies and at the shoulders must be made of compounds that have lower heat retention.
These things combined, more or stronger cap plies and better rubber compounds in key places, increase the cost of higher speed rated tires.

Image source: The Role Of Cap Plies In Steel Belted Radial Tires [pdf], David Osborne

Nice answer. Any chance you might be able to find a larger copy of that image? That's tiny!

@FreeMan Did that help any?

@FreeMan The image was embedded in a pdf file. I took a screenshot and cropped it down. Plus it wasn't very clear to begin with

Excellent, thanks Tom!


text:
Why does wake turbulence seem to move upward on touchdown?

Source of the first photo
I saw this photo of business jet touching down (first picture) and the smoke of tires forming wake turbulence . as I have provided other pictures (second and third) of "what we have seen and know about the theory of wake turbulence" , you can see this strange upside down form of wake turbulence . simply what is the reason ?

Unless you made these great pictures yourself, please provide attribution.

sorry couldn't work with tags and brackets , "stackexchange" can provide and easier uploading mechanism though .

No it was fine the way it was (images visible), but just provide a link to where you got the pictures in the first place, in the text below. And agreed, it's sometimes a bit confusing.

oh I'm so sorry , misunderstood . here is the link sir : http://www.mg-aviationphotography.com/uploads/9/8/4/5/9845374/global-express-1_orig.jpg

we would need the source also of the other 2 photos. thanks :)

http://imgur.com/BcZ60cM                https://pbs.twimg.com/media/C7vOpthVwAAGdWs.jpg

Actually, yes, it is "upside down" as compared to the respective wing-tip vortices.
Your picture shows the vortices coming off of the horizontal stabilizer,

which rotate in the opposite direction of the wing tip vortices that come off of the wing tips. Notice in your original pictures, the 2nd and 3rd pictures show the wing-tip vortices off of the airplanes right wing (as viewed from the front) rotate counter-clockwise. However, in the top picture the right vortex rotates clockwise.
That is because the horizontal stabilizer (along with the elevator in the UP position) is basically acting like an upside down wing defecting air upwards (as the picture illustrates). The high pressure region on the horizontal stabilizer on landing is on the top, while the high pressure region on the wing is on the bottom. This accounts for the opposite direction of rotating between wing tip vortices vs horizontal stabilizer vortices. The upwardly deflected elevator deflects the relative wind upward at the tail causing that upward movement of the rubber smoke.The picture is cropped so we can't see the wing-tip vortices (assuming there was dust or smoke in the air to view them).
Peter Kämpf posted an amazing GIF here showing a slow motion flight of a model 747 going through smoke that shows this process. Its difficult to see, but for a brief moment after the aircraft passes through the smoke, you see the hint of the horizontal tail vortices trying to rotate and go up, but they are washed out by the enormous downwash of the wings.

@ymb1 Thank you! That is the correct gif! If you watch it carefully (an repeatedly) you will see faint opposite vortices coming off of the horizontal stabilizer, but they are overwhelmed by the massive downwash of the main wings. Its pretty amazing.


text:
During autoration, does it help to pump the cyclic to increase the RPM?
I have heard of the idea of moving the cyclic forward and backwards in order to get an increase in rotor RPMs. Does anyone have any information on this as to when you would use it or airspeeds it would only be effective at?
Scenario is low altitude autorotation/unpowered flight:

About a 100 - 150 feet AGL, super slow (say 10 - 20 kts)
  You lose an engine there.
  The ideal thing would be to get as much airspeed as
  possible to reduce that sink rate as compared to a vertical descent /
  pull collective / do a hard run on.
However presuming you had to come straight down (trees, power lines or
  whatever) I have heard from more than one source that pushing the
  cyclic back and forth at quick segments will help build RPM's but I
  just couldn't figure out how.

I can see you having a momentary change until the governor kicks in and corrects the rotor RPM, but you shouldn't deviate too much.

In an autorotation

Wes, do you perhaps mean pushing forward on the cyclic to pitch down for more airspeed, and—once a little airspeed has built up—pulling back to convert that airspeed to rotor RPM? That sounds plausible, but not something I know much about (@Simon, care to chime in?). What I just described sounds like a slower maneuver than what you seem to have described, Wes.

Hey Jonathan, well the scenario is about a 100 to a 150 feet agl and super slow say ten to twenty kts. You lose an engine there the ideal thing would be to get as much airspeed as possible to reduce that sink rate as compared to a vertical descent pull collective and do a hard run on. However presuming you had to come straight down trees, power lines or what ever I have heard from more than one source that pushing the cyclic back and forth at quick segments will help build RPM's but I just couldn't figure out how

Are you unhappy with the answer you got here?

What sources?  I cannot think of any advantage to doing this since  every control input takes energy out of the system through losses.  I can imagine an initial flare to preserve or re-gain RRPM followed by stick forward to gain airspeed all the way down to the final flare but backwards and forwards is not going to  help.

BTW, that slow at that height is likely not survivable.  You will have around 8 seconds, perhaps about 5 at 100 feet before you are on the ground.  To gain airspeed for the flare will need nose down all the way.

@Simon In a lot of helicopters that will bring a loss of Nr with initial Fwd Cyclic, and if it has a teetering head will likely unload the head with the risk of mast bumping, and possibly a blade going divergent and hitting your tail pylon. (Some Robinsons are vulnerable to that...depending on a number of factors and the situation).

What Simon says

@KorvinStarmast I wasn't thinking about stick forward enough to unload the disk!  Just to gain airspeed but I can think of no advantage to "pumping" the cyclic and stick forward for airspeed at the height the OP is asking about would be a one off adjustment.  You would only have enough time to gain speed down to 50 feet for maybe 2 or 3 seconds before the flare.

@Simon I hear ya, I was just trying to picture in my head the situation was not sure of the magnitude of control deflections being considered.  Your point on where in the H-V diagram the situation presents itself is spot on. (I think I address it in my answer).

Cyclic pumping will likely degrade your performance
As explained here, it leads to rotor inefficiencies

As far as moving the cyclic around goes it destroys lift as the TRT
  vector is all over the place and not acting in one place or close too
  it and more power is required

What is this TRT he's talking about?  Total Rotor Thrust

In a still air hover, TRT is, in broad terms, equal and opposite to
  weight. As the disc is tilted to commence a transition into forward
  flight, the TRT vector is tilted and must be increased so that its
  vertical component remains equal to weight if level flight is to be
  maintained.

With the above in mind, pumping the cyclic with the engines working simply means that you need more power from your engine to keep your Nr up to fly, as you are being inefficient.
If you have no power, pumping the cyclic is counter productive to your efforts at maintaining Nr since the back and forth creates sequential inefficiencies, and more drag but you have no engine to restore Nr... and in the situation you describe, your precious Nr is a critical resource to your walking away from the forced landing or crash.
Depending on what is happening, a slight turn or flare (aft cyclic, not foreward) may load the head and preserve Nr a bit so that it's still turning with enough inertia to help you as you near the ground and need that cushion from the collective as you hit the ground.  Each bit of Nr you retain for that last pull is critical, in that situation.
It's a tough one, the low speed, not-quite-inside-the-Hv-diagram scenario that you presented.
Consult the manual for your model helicopter, and the H-V diagram.  Know your limitations.

I appreciate the feedback! You explained it very well to me! Thanks

@Wes glad to be of help.


text:
Is there a surface of a commercial jet exposed to air flow at speed near Mach 1?
With commercial aircraft flying slightly above Mach 0.8, is there any surface exposed to speed of air significantly larger, e.g. near Mach 1? ignoring:

The engine components,
The boundary layer as clarified by Trebia Project.

Edit: Reading useful information provided in comments and answers, I realize the key notion is "critical Mach number", and the question boils down to:

Are commercial jets flying at critical Mach number speed or higher?

since the critical Mach number speed is -- by definition -- the one at which some airfoil portion experiments a supersonic airflow. See also:
How does exceeding the critical Mach number of an aircraft affect its operation?

The outside.

Fair enough. +1. I updated the speed to near Mach 1.

Flow speed through engines will be much slower than mach 1 (excepting scram/hyperjets).  For highest velocity flow look for lifting surfaces (e.g. the wing) and propeller tips.

@casey Yes, flow through the engines is slower than Mach 1, but the fan blade tips themselves exceed Mach 1 on many turbofan designs, resulting in shockwaves, which I'm assuming is why mins excluded the engines from consideration.

http://aviation.stackexchange.com/questions/11884/do-nacelles-around-aircraft-engines-helps-in-reducing-the-engine-sound This answer states the blades of engines runs at mach 1.5

Since the A310 new jet aircraft use supercritical airfoils, and they have their name from flow speeds above the critical speed at their design point. Speeds of up to Mach 1.2 are possible and are normal in everyday operations.

@fooot Here is another picture of one of the optical effects of shockwaves generated by commercial craft: http://www.pprune.org/tech-log/443649-0-98-mach-747-8-a.html#post6264909. I have seen this several times while traveling as a passenger, and in one case, the wave was visible as a distortion of the view through it (this was on a Tu-154, which I don't think has a supercritical wing.)

Of course! If you check the wikipedia page the Critical Mach Number of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it.
The Drag Divergence Mach Number is usually bigger than the Critical Mach Number, it means that at that speed there are big surfaces exposes to speed of air larger than 1.
It can happen because the figure of an airplane is shaped in order to avoid shock waves with flow and to postpone the maximum as possible the Drag divergence Mach number (in order to have a greater cruise speed).
Where?
On the upper part of the wings, where the flow is accelerated in order to produce lift.
Clarification about engines (thanks to the help of one of the comments):
The flow from a jet engine has a speed about double of the cruise speed of the airplane. Anyway the outflow from an airliner jet engine is much hotter than the surrounding air, so the speed of sound in this gas stream is much higher; its Mach number is still subsonic.

it doesn't hit any surface -- unless you consider the engine wall a surface ;)

The outflow from an airliner jet engine is much hotter than the surrounding air, so the speed of sound in this gas stream is much higher. While you are right that the gas speed is about twice the flight speed, its Mach number is still subsonic.

If we take the question as it is, I will say that never ever any point of the surface of any airplane will be at Mach > 1. Close to the surface, at typicial airliner, exist an thin layer of air that adapts the speed from outside to the speed of the airplane. So, the air at the surface of the airplane is at velocity relative to the airplane of 0. So the Mach = 0.
This layer is called boundary layer and, in typical airliners, some centimeters over the the edge of the surface of the airplane the air will recover the speed and everything that has been mentioned will apply (and so there will be points close to the surface where the Mach will be > 1).
Question seems as well focused in the cruise condition, however, when high lift devices are deployed (flaps and slats) the acceleration on the upper surface is much bigger, you can have one or several points "close to the surface" where the Mach is 1 having the airplane flying at relatively low Mach number (0.3-0.5). This depends strongly of the high lift devices used by the airplane.

Added a comment about high lift devices, also potentially having Mach 1 at low speed


text:
Can spatial disorientation in low visibility situations lead a pilot to fly upside down?
In this comment it's mentioned that pilots in instrument conditions may wind up in a situation where they're inverted due to spatial disorientation, and be completely unaware of it until they fly out of the cloud.
Is that really something that can happen so easily?

A untrained pilot in unexpected IMC won't survive for 3 minutes.

One of the flight instructors I took lessons from told me this actually happened to him (he took off into clouds and his artificial horizon died as soon as he was in the soup)...he popped out a few hundred feet later "at a crazy angle"...

huh, why does the AI always fail the second you go into the soup?

Isn't this exactly what happened to JFK Jr.? As shown in this week's Air Crash Investigation/Mayday.

@DannyBeckett: According to wikipedia, yes it was spatial disorientation.

@rbp: Blame Murphy.

The short answer is "Yes", if the pilot is not properly trained, doesn't trust their instruments, or has an instrumentation failure.
Without a visual reference (such as the real horizon or artificial horizon) it's very easy for a pilot to place their aircraft in an "unusual attitude" -- something other than the expected straight-and-level flight or commanded turn.
As humans we naturally rely on our inner ear and sense of balance to tell us what's "up" or "down", but in a moving aircraft you can move through a whole range of attitudes in "1G maneuvers" (where your body thinks down is where your seat is).
Little micro-movements we unconsciously make on the controls (or larger movements we may make consciously in response to turbulence or other perceved disturbances in the aircraft's attitude) based on what our ears and butts are telling us will eventually get us into trouble.
It's so easy that often instructors will have students create their own unusual attitudes in training by having the student close their eyes and simply try to fly straight and level - within a few minutes at most the student will invariably no longer be in level flight.

There's an exercise you can do on the ground to illustrate how imperfect your sense of balance and direction is, but it requires a large, flat, open area. We'll use an American Football field for this example:

Stand on one of the goal lines
Have a friend stand at the 50 yard line (about 45 meters away)
Close your eyes or put on a blindfold, count to ten, and walk directly toward your friend
Stop when you reach your friend (or your friend yells "STOP" because you're about to walk into a goal post)

Most people will not make it to their friend on the 50 yard line, because without a visual reference it's very hard to walk a straight line: You will veer off one way or the other, and some folks will even manage to walk in a complete circle (which is what eventually tends to happen over a large enough distance).
The same principles apply to flight, except there's a third dimension (vertical) to contend with.

And note that walking with closed eyes is still a lot easier, because the only motion is due to your legs and your brain can correct by correlating position and forces exerted by your legs. In an aircraft your platform is moving with you, so that this only adds to the confusion instead.

Yes, definitely. This is from an NTSB accident report:

During the right turn, the pilot stated that he looked to his right
  to cross check the GPS and set up the autopilot for a coupled
  approach. He felt the airplane start to accelerate rapidly, and he
  looked back to the Primary Flight Display (PFD) which was “showing all
  brown with no sky and 6-7 chevrons, indicating a severe unusual
  attitude.” He tried to correct the unusual attitude, but said that he
  had severe vertigo, and was unable to regain control of the airplane.
  He elected to deploy the ballistic recovery parachute, and the
  aircraft impacted terrain in a nose low attitude in a creek bed.

The roll wasn't fully inverted, but it was extreme (120 degrees to the left):

The downloaded data showed that, just prior to the accident, the
  airplane went through a series pitch and roll oscillations, with
  maximum pitch values of approximately 26 degrees nose up, and 75
  degrees nose down. The airplane reached maximum roll values of
  approximately 83 degrees right wing down, and 120 degrees left wing
  down.

So yes, it's absolutely possible for the aircraft to end up in an extreme attitude very quickly and easily: in this case the pilot just looked away to set the autopilot. The reasons why this can happen so easily have been discussed and commented in detail in this question.

and pulling out of a 75-degree dive is how you break the wings off

Yes. Remember that once you get into a weird position, like upside down, you may be turning at the same time, creating a false gravity, so it does not feel like you are upside down. Usually you just feel "cockeyed", and if you try to adjust based on that "feeling", you will make the WRONG input which will make the situation worse. If you strap yourself inside a ball in an amusement park and get turned upside down, even then it can be difficult to tell exactly what is going on.
Many pilots have difficulty trusting their instruments and have to be trained to do so very strictly. When I was put "under the hood" for the first time, my instructor told me "you will go into a spin". I said "no I will not". He said, "Yes you will, everybody does the first time." As a matter of fact I kept the plane straight and level and did not go into a spin, but I was an exceptional case, 95% of students will start spinning the aircraft uncontrollably if they cannot see the horizon. JFK, Jr. was killed that way.
Let me just say, that first time under the hood I was sweating bullets and focusing my mind like I was trying to play speed chess against Bobby Fischer. Flying by instrument is INSANELY hard, if you have not trained on it for hours and hours. You have 5 different needles that you have to keep lined up at the same time. Even experienced pilots find manual instrument flying grueling and mentally taxing (thank god for autopilot).

FWIW: I've been told, and tend to agree, that PPLs who play Flight Simulators more are more comfortable looking at and interpreting the instruments, because we get no sensory cues from our desk-chairs. :)

"spin" or "spiral"?  I suspect your instructor said or meant to say graveyard spiral

Yes, very easily... Although 'sideways, nose down and at 200 knots into the ground before becoming a massive fireball' is more common
If it's only a short period they may just find themselves coming out of the other side of the cloud at a completely different attitude than they went in (and, likely, altitude too), but with anything more than just a quick cloud, it can be far more serious.
Pilots without an instrument license have something like a 3 minute life expectancy once they get into instrument conditions.

Before I flew into a cloud I thought I could trust my senses just a tiny bit.  When I came out the other side, my attitude was completely different in more than one way.